Peptides are ubiquitous biological molecules and have, in recent years, become the subject of extensive research and investigation. For example, the possibilities for utilizing natural biological substances, such as peptides, as therapeutics for various disease states is being aggressively explored.
Elucidation of the amino acid sequences of such peptides such as Growth Hormone, Growth Hormone Releasing Factor, or Cholecystokinin (CCK) has lead to advancements in the understanding of how these molecules work in treating various disorders. However, peptides suffer from rapid degradation upon exposure to the internal milieu often resulting in low bioavailability. It has been recently discovered that in many instances if the amino acid constituency of many naturally occurring peptides is altered by single or multiple amino acid substitutions at different sites, the analogs of the natural peptide may degrade less rapidly and hence exhibit greater bioavailability and efficacy.
For example, CCK is a family of peptide hormones which vary in length up to 58 amino acids. The sequence of CCK first discovered contained 33 amino acids. CCK as well as fragments thereof, such as CCK-8 and CCK-7, have been shown to have satiety-inducing effects when administered peripherally to animals. CCK-8 has the amino acid sequence: ##STR1## CCK-7 lacks the 26-position amino acid Asp.
While CCK analogs are known to have satiety inducing effects, they exhibit low bioavailability and are poorly absorbed. Tyrosine sulfate containing peptides are well known to suffer loss of the sulfate moiety upon storage, particularly when in solution. This has led to the synthesis of various CCK analogs wherein the attempt to improve properties such as stability and bioavailability has been made. A multitude of CCK analogs with various amino acid substitutions have yielded compounds with altered properties which enhance their potential usefulness in human therapeutics.
The instant invention comprises analogs of Tyrosine Sulfate or Tyrosine Phosphate containing peptides. Examples of Tyrosine Sulfate containing peptides include peptides such as gastrin, cholecystokinin, platelet factor 4, or hirudin. Many Tyrosine Phosphate containing peptides are also known such as human insulin receptor, progesterone receptor, or Lipocortin-I. All of these peptides may yield analogs according to the instant invention.
For example, Tyrosine Sulfate occupies the 27 position amino acid of CCK or its shorter analogs such as CCK-7 and 8. When this Tyrosine Sulfate is substituted by a radical of the invention, the result is a CCK analog which may exhibit greater bioavailability, and hence may lend itself more readily to absorbtion following oral administration.